The present invention relates generally to control arrangements and more particularly to float switches.
There are already known various float switch constructions, among them such which include a housing which is manufactured with the use of a closed-pore integral foam, an electric switch positionally fixed in the housing, a gravity actuation arrangement which actuates the electric switch, and a current supply cable having an end portion which is fixed in position with respect to the housing and the connection zone of which to the electric switch is embedded in such a manner as to be protected against penetration of moisture therethrough.
The heretofore known float switch constructions of the type described above obtain the buoyant force which is needed for their floating capability as a result of the formation of air chambers of sufficient volume in the interior of the float housing. A typical example of float switch arrangement constructions of this type is disclosed, for instance, in the German published patent application DE-OS 27 44 404, in which the electric switch and the gravity actuation arrangement are accommodated in an encapsulated inner housing into which a connecting zone of a current supply cable is inserted. This inner housing is then surrounded at a distance by a second, outer housing which is also encapsulated. In this construction, the connection zone of the electrical conductors of the current supply cable, which is situated in the interior of the inner encapsulated housing, is filled with a molded material in such a manner as to be impervious to moisture.
While adhering to the principles of double housing construction of the float housing and of achievement of the floatability of the float switch arrangement by a sufficient air chamber dimensioning, it has also been already proposed, for instance, in the German Utility Model DE-GM 76 04 668 to make the outer housing of an integral foam which closely surrounds the inner housing, the integral foam being of the type having closed pores. Herein, the integral foam layer is so chosen that the specific weight of the housing is held so low that the housing remains floatable despite the presence of the additional synthetic plastic material layer, due to the provision of the air chamber in the inner housing.
Float switch arrangements of this kind are very often used outside, where they are often subjected to considerable temperature variations. Now, it has been established that, in the heretofore customary float switch arrangement constructions, considerable pressure variations toward the superatmospheric pressure or toward the subatmospheric pressure may occur in the quite sizable air chambers contained in the respective float switch arrangement interiors. Such pressure variations not only deleteriously influence an exact response of the float switch arrangement, but also exert so-called "pumping effects" on moisture precipitated in the current supply cable which is also subjected to such temperature variations, as well as in the electric conductors of the current supply cable, so that, despite the encasement of the connection zone of the electric conductors, there can still occur drawing-in of moisture not only out of the jacket of the current supply cable, but even out of the small insulated electric conductors.